An electric field is associated with a scope of a force to move electric charges in a space and a distribution thereof and is a source of an electric force. The electric field is divided into an electrostatic field caused by electric charges collected in a specific position and a time-varying electromagnetic field caused by electromagnetic waves. The electrostatic field is determined by an amount of electric charges accumulated in a specific position, and accordingly does not change unless the amount of electric charges changes. The time-varying electromagnetic field is a time-dependent electric field that has a magnitude changed based on a waveform of a radio wave. Due to the above difference, the above electric fields are measured using different methods. To measure the electrostatic field, a method of measuring a potential difference between two electrodes is generally used. To measure the time-varying electromagnetic field, a method of measuring an induced current that flows via an antenna is used.
An importance and frequency of use of electric field measurement apparatuses are increasing due to a generation and applications of various electric fields, for example, a malfunction of electronic equipment due to electromagnetic leakage of electrical products and electronic components, an influence of use of various frequencies on a human body due to a development of a wireless communication technology, and a medical utilization such as a motion sensor using a body capacitance, a positron emission tomography (PET) or magnetic resonance imaging (MRI) which uses a body reaction due to external factors, electroencephalogram (EEG) and electrocardiogram (ECG).
However, since the electrostatic field and the time-varying electromagnetic field are different in a measurement principle from each other, measurement results of the electrostatic field and the time-varying electromagnetic field may be considerably constrained. For example, in a system using an alternating current (AC) and direct current (DC) at the same time, a combination of the electrostatic field and the time-varying electromagnetic field may have a great influence on a specific point in time, however, it is difficult to measure a magnitude of the above composite electric field using a general electric field measurement apparatus. Also, in an antenna that is a measurement apparatus used to measure the time-varying electromagnetic field, a band of a target frequency to be measured is generally fixed due to a shape of the antenna. Accordingly, a utilization of the antenna as a measurement apparatus may be inevitably reduced in a modern wireless communication environment.
In addition, an existing electric field measurement apparatus has a difficulty to measure a very weak electric field. For example, when a brain wave is measured, an intensity of an electric field emitted to the outside is extremely low, because a skull has an electric field shielding effect. Thus, an apparatus for measuring an electric field needs to include an amplifier, however, an amplification rate is limited at all times because noise generated in the amplifier becomes stronger as the amplification rate increases. Here, a circuit to distinguish a signal from noise is additionally required.
Moreover, the existing electric field measurement apparatus is generally incapable of measuring a direction of an electric field and has a characteristic that a measurement result of a magnitude of the electric field varies depending on a phase of a measurement apparatus. For example, when a phase of an antenna included in a measurement apparatus for measuring a time-varying electromagnetic field does not match a phase of an electromagnetic wave that causes a time-varying electromagnetic field, a magnitude of an induced current that flows through the antenna may decrease, and accordingly a magnitude of a measured electric field may be less than an actual magnitude. Thus, when a single sensor is used to measure an electric field, the electric field may need to be measured several times by slightly changing a phase of the sensor to accurately measure an intensity and direction of the electric field, and each of measurement results may need to be integrated and analyzed, which may cause an inconvenience.